Although there has been relatively little work on 12-step treatment for seriously mentally ill patients, extant literature indicates that dually diagnosed individuals attend traditional 12-step programs such as AA, NA, and CA at rates comparable to singly diagnosed substance abusers, and that participation is associated with decreases in substance use. Specialized 12-step programs for the dually diagnosed, developed over the past 10 years, may offer additional benefits. In order to maximize the effectiveness of specialized and traditional 12-step programs for dually diagnosed individuals, specially adapted 12-step facilitation (TSF) treatment for the dually diagnosed should be developed and tested. Standard TSF should be modified to address the special needs of dually diagnosed individuals, mesh with specialized 12-step programs available in the area, and address barriers to attendance, participation, and engagement experienced by the dually diagnosed. We have developed a modified TSF based on the Project MATCH TSF manual. Modifications to this 12 week individual therapy include: emphasis on specialized 12-step program attendance; readings primarily from specialized 12-step program literature; participation in the second session by a community specialized 12-step program member; case management to assist participants in finding and attending meetings; omission of work on the fourth step; and the addition of topics covering medication compliance and specific social skills needed to negotiate 12-step meetings. In a pilot study with 10 dually diagnosed individuals, participants showed significant decreases in substance use and significant increases in 12-step attendance after receiving the specialized TSF. Building on this pilot study, the proposed study is a larger Stage Ib study of the modified TSF for seriously mentally ill patients engaged in dual diagnosis treatment. Participants with a psychotic or major affective disorder will be randomized to modified TSF (n=90) vs. treatment as usual (n=45). Participants will be followed for a total of 48 weeks. Assessments will include rigorous diagnosis and measures of alcohol and other drug use, consequences, psychiatric symptoms, 12-step behaviors, 12-step specific and non-specific change mechanisms, and social support. Specific Aims of the study include assessment of the integrity of the planned intervention and assessment battery; tests of the effectiveness of the adapted TSF relative to treatment as usual; determination of whether psychiatric diagnosis moderates treatment response; and investigation of causal mechanisms of response to treatment.